A cat that fights nail trims is not being difficult. It has learned, usually through a few rushed early experiences, that the clipper means restraint and an odd pressure on its paws. That association is what you are changing, not the cat's personality, and not its tolerance for being handled in general. Desensitisation and counter-conditioning are the two learning principles at work here. Desensitisation means exposing the cat to the thing it dislikes at an intensity low enough that it does not react. Counter-conditioning means pairing that exposure with something it actively wants, usually food, until the neutral or negative thing predicts the good thing instead.
